1-Cyclopropyl-6,8-difluoro-1,4-dihydro-4-oxo-quinoline-3-carboxylic acids having a piperazino or an N-methylpiperazino group at the 7-position are known from German Offenlegungschrift No. 3318145 and Belgian Pat. No. 899,399. The compounds are described as broad spectrum antibacterial agents.
5-amino-1-ethyl-6,8-difluoro-1,4-dihydro-4-oxo-7-piperazinyl-quinoline-3-ca rboxylic acid is described in Japanese Patent Publication No. 58:174,367. Copending U.S. application Ser. No. 770,897 of Aug. 30, 1985, describes a group of 5-amino-1-cyclopropyl-6,8-difluoroquinolones as broad spectrum antibacterial agents. The amino substituents at the seven-position are limited to pyrrolidines and spiroamines.
It was thus surprising and unexpected to discover that the heretofore never described 7-piperazino and 7-N-methylpiperazino derivatives of 5-amino-1-cyclopropyl-6,8-difluoro-1,4-dihydro-4-oxo-quinoline-3-carboxyli c acid have not only good broad spectrum antibacterial activity in general but especially better activity against Pseudomonas aeruginosa, an important and hard to kill bacteria in antibiotic therapy.